Objective: The purpose of this protocol is to characterize abnormalities in motoneuron recruitment in adult patients with corticospinal tract dysfunction using electrophysiologic measures. We wish to determine whether the intrinsic spinal mechanisms for recruitment are abnormal or whether only inputs to motoneurons are changed. This information is pertinent for assessing ways that can ultimately be used to enhance strength in patients with corticospinal tract dysfunction using the existing spinal circuitry.